Spin-coated films of cellulose acetate (CA), cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB) and carboxymethylcellulose
acetate butyrate (CMCAB) have been characterized by ellipsometry, atomic force microscopy (AFM) and contact angle measurements.
The films were spin-coated onto silicon wafers, a polar surface. Mean thickness values were determined by means of ellipsometry
and AFM as a function of polymer concentration in solutions prepared either in acetone or in ethyl acetate (EA), both are
good solvents for the cellulose esters. The results were discussed in the light of solvent evaporation rate and interaction
energy between substrate and solvent. The effects of annealing and type of cellulose ester on film thickness, film morphology,
surface roughness and surface wettability were also investigated.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
The Suzuki–Miyaura coupling polymerization of dibromoarene 1 and arylenediboronic acid (ester) 2 with a Pd catalyst having a high propensity for intramolecular catalyst transfer is reported. The polymerization of excess 1 with 2 affords high‐molecular‐weight π‐conjugated polymer having boronic acid (ester) moieties at both ends, contrary to Flory's principle. This unstoichiometric polycondensation behavior is accounted for by intramolecular transfer of the Pd catalyst on 1 . In the polymerization of 1 and 2 having different aryl residues, high‐molecular‐weight polymer is obtained when the stronger donor aromatic is used as the dibromo monomer and the weaker donor or acceptor aromatic is used as diboronic acid (ester) monomer. The pinacol boronate moieties at both ends of the obtained poly(p‐phenylene) (PPP) can be converted to benzoic acid ester, hydroxyl group, and bromine. Furthermore, the reaction of the pinacol boronate‐terminated PPP with poly(3‐hexylthiophene) (P3HT) having bromine at one end yields a triblock copolymer of P3HT‐b‐PPP‐b‐P3HT.
A bis(imidazolidine)pyridine (PyBidine)–Cu(OTf)2 complex catalyzing the endo‐selective [3+2] cycloaddition of nitroalkenes with imino esters was applied to the reaction of methyleneindolinones with imino esters to afford spiro[pyrrolidin‐3,3′‐oxindole]s in up to 98 % ee. X‐ray crystallographic analysis of the PyBidine–Cu(OTf)2 complex and DFT calculations suggested that an intermediate Cu enolate of the imino ester reacts with nitroalkenes or methyleneindolinones, which are activated by NH‐hydrogen bonding with the PyBidine–Cu(OTf)2 catalyst. 相似文献
Polymer-supported catalysts have been of great interest in organic syntheses, but have suffered from the difficulty in obtaining direct structural information regarding the catalyst species embedded in the polymer due to the limitations of most analytical methods. Here, we show that dynamic nuclear polarization (DNP)-enhanced solid-state NMR is ideally positioned to characterize the ubiquitous cross-linked polystyrene (PS)-supported catalysts, thus enabling molecular-level understanding and rational development. Ammonium-based catalysts, which show excellent catalytic activity and reusability for the transesterification of methyl esters with glycidol, giving glycidyl esters in high yields, were successfully characterized by DNP 15N NMR spectroscopy at 15N natural abundance. DNP 15N NMR shows in particular that the decomposition of quaternary alkylammonium moieties to tertiary amines was completely suppressed during the catalytic reaction. Furthermore, the dilute ring-opened product derived from glycidol and NO3− was directly characterized by DNP 15N CPMAS and 1H–15N and 1H–13C HETCOR NMR using a 15N enriched (NO3) sample, supporting the view that the transesterification mechanism involves an alkoxide anion derived from an epoxide and NO3−. In addition, the detailed analysis of a used catalyst indicated that the adsorption of products on the cationic center is the major deactivation step in this catalysis.We demonstrated that DNP-enhanced NMR spectroscopy enables the direct and detailed characterization of polymer-supported alkylammonium catalysts. 相似文献
Interaction and stability of binary mixtures of cationic surfactants hexadecyltrimethylammonium bromide (HTAB) or hexadecylpyridinium bromide (HPyBr) with nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) have been studied at different mole fraction of cationic surfactants by using interfacial tension measurements and fluorescence probe techniques. From interfacial tension measurements, the critical micellar concentration and various interfacial thermodynamic parameters have been evaluated. The experimental cmc's were analyzed with the pseudophase separation model, the regular solution theory, and the Maeda's approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTAB + Mega-10 were obtained. It has been observed that the aggregation number of mixed micelles deviates negatively from the ideal behavior. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio and found to be increase with the increase of ionic content. The polarization of fluorescence probe Rhodamine B was monitored at different mole fraction of cationic surfactants. 相似文献
The nanostructural design of heterogeneous catalysts has often been demanded for assessing synergetic effects, which should be developed further by using high-surface-area porous metal oxide supports. However, such opportunities have been undermined by the poor stability of ordered mesoporous structures. Herein, rational design is demonstrated to obtain nanocomposite catalysts showing improved NOx storage properties owing to the presence of Ba species over a well-designed mesoporous alumina (Al2O3) support. It is found that Ba species are impregnated successfully only after the stabilization of the mesoporous structure by full crystallization of Al2O3 frameworks to the γ-phase, with the formation of Pt nanoparticles coinciding with complete removal of organic components. All the insights during this synthetic procedure are essential for designing high-performance catalysts to purify and recover NOx molecules, and are applied for designing a variety of cutting-edge mesoporous nanocomposite catalysts. 相似文献
Rotation times of perylene and 8-methoxypyrene-1,3,6-trisulfonate (MPTS) in 1-alkyl-3-methylimidazolium tetrafluoroborate and 1-alkyl-3-methylimidazolium hexafluorophosphate under high pressure have been examined by means of time-resolved fluorescence anisotropy measurements. The isothermal compression of sample solutions by the application of high pressure can change the solvent viscosity alone over a wide range, allowing for an observation of the pure viscosity dependence of rotation times at a constant temperature (45 °C). Rotation times of both perylene and MPTS show a considerably nonlinear dependence on the solvent viscosity and a substantial deviation from the predictions of hydrodynamic and quasihydrodynamic theories, particularly at high pressures. 相似文献